SQL Migrations are the accepted method for OpenStack projects to ensure
that a given schema is consistent across deployments. Often these
migrations include updating of the underlying data as well as
modifications to the schema. It is inadvisable to perform a downwards
migration in any environment.

Best practices state: when reverting post schema migration the
correct course is to restore to a known-good state of the database.

Many migrations in OpenStack include data-manipulation to ensure the data
conforms to the new schema; often these data-migrations are difficult or
impossible to reverse without significant overhead. Performing a downgrade
of the schema with such data manipulation can lead to inconsistent or
broken state. The possibility of bad-states, relatively minimal testing,
and no demand for support renders a downgrade of the schema an unsafe
action.